Technical Pamphlet for Workmen - Magneto

The early telephones worked on the Magneto system.  The telephone was wired to a central switchboard that would connect the caller to another telephone via cords.

The telephone microphone was powered by a local battery and called the exchange switchboard by means of a hand generator.  The switchboard would also call telephones by the use of a hand generator.  On finishing a call both users would go on hook and then crank their generators to signal to the exchange switchboard that they had hung up (this is known as ringing off).

Magneto Telephones
On lines within the same building, the battery-ringing telephone is generally adopted, owing to its cheapness.  On long lines it is necessary to introduce a relay to economise battery power, and in such circumstances the magneto-ringing telephone is generally preferred. It will be seen that the transmitter, the primary of the induction coil, and the speaking battery form a local circuit.  This circuit may be closed either by a gravity switch or a microtelephone press key.  With the telephone resting, the magneto bell in series with a condenser is connected across the lines via the contacts of a switch forming part of the magneto generator and a second switch forming a portion of the gravity switch.  When the handle of the magneto generator is turned, the bell is disconnected and the generator is connected across the A and B wires.  When the receiver or microtelephone is removed from its rest, the local speaking circuit is closed, the magneto bell disconnected from the line, and the receiver in series with the secondary winding of the induction coil is connected across the A and B wires.  The method in which these circuit changes are effected in the types of telephone instrument used in a magneto system varies considerably, but the principle remains the same.

GPO Exchange Codes

These are the codes, used in the List of Exchanges, to indicate the type of equipment in use.

Type of Exchange 1930 1936
Magneto, Self-Restoring Indicators C M
Magneto, Hand-Restoring Indicators D M
Magneto, Ring Through System on Lamps E M
Magneto, Hand-Rest., Auto-Clear Indicators/Lamp F M

Outgoing Calls

A subscriber calls the exchange by means of the generator provided for the purpose. On the call being answered and the connexion to the called subscriber's line, assuming it is disengaged, being completed, the two subscribers are enabled to speak.  Power for the transmitters is supplied by local batteries

On the conclusion of conversation, the subscriber, after replacing the receiver, gives a generator ring as an indication to the exchange that the call has terminated and the ringing. current operates an indicator or relay associated with the exchange cord connecting circuit.


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Last revised: February 26, 2023